As a testament to humankind’s everlasting quest for knowledge and understanding of the self, a number of scientific studies in the recent times have examined the elusive relationship between the human brain and that fountainhead of human emotion and passion, namely, Religion. There have been studies on neurological correlates of religious experiences and spiritual practices, such as meditation and prayer; many studies have looked at both acute and chronic effects of such practices in relation to brain function. A recent study along the same lines, published by Owen et al. of Duke University, in PLoS One on March 30, 2011, has attempted to link religious factors with changes in a specific brain region, the hippocampus, using functional magnetic resonance imaging (fMRI) techniques.

The hippocampus, located in the medial temporal lobe of the brain, is a component of the limbic system with several functions, such as memory consolidation, contextual and episodic learning, spatial navigation, as well as generation of attention and emotion, through interconnections with another limbic system component, amygdala. Measurements of hippocampal volume has been linked to clinically relevant neurological outcomes, such as depression, dementia and Alzheimer’s Disease.

Owen et al. used high resolution MRI to measure the volume of the hippocampus in the 268 study subjects, both male and female, aged 58 years and up. The subjects were assessed primarily on religious factors, such as life-changing religious experiences (LCREs), participation in spiritual practices, and membership in a religious group, as well as on other psycho-social (stress, social support and depression status) and demographic (age, sex, self-reported white/non-white status, years of education, and duration in the study) covariates.

Interestingly, the study found an association between certain religious factors and longitudinal changes in hippocampal volume during late life. The volume of the hippocampus was significantly reduced (what the authors termed as “hippocampal atrophy”) bilaterally, over time in subjects identified as born-again Protestants and Catholics, when compared with Protestants who were not born-again. Greater hippocampal atrophy was also observed in subjects reporting LCREs. These longitudinal associations were not influenced by baseline psychosocial or psychiatric factors, or study subject demographics.

Importance of hippocampus in religious or spiritual beliefs and practices has been highlighted in several previous studies. Hippocampal activation, along with higher gray matter concentration and volume, has been noted in PET scans and MRIs in meditative states; the phenomenon of hyper-religiosity observed in temporal lobe epilepsy is positively correlated with hippocampal atrophy. [references are in the cited PLoS article under discussion]

Paradoxically, however, the hippocampal volume was found to be also reduced in those subjects who reported “no religious affiliation”.

Establishment of a causal relationship between the brain and a nebulous variable such as religion or religiosity is by no means easy. In the PLoS study, the authors have interpreted the observations in terms of stress and its cumulative effect on the hippocampus. There is evidence that stress alters brain structure and function. It is possible that either stress or stress-induced cortisol or both may influence the structure and function of the hippocampus, and the authors surmise that the reduction in hippocampal volume observed in the “born-again” as well as LCRE subjects and the “no religious affiliation” subjects may be related to the stress of belonging to what they term as “religious minority groups”.

The authors have outlined how religious experiences can serve as stressors:

Spiritual experiences not easily interpreted within an existing cognitive framework or set of religious beliefs have been shown in previous research to be detrimental to subjective well-being. Such experiences have the capacity to produce doubts regarding previously unquestioned convictions, potentially inducing cumulative stress even if the experience was subjectively positive. If the experience prompts a change in religious groups, existing social networks may also be disrupted. Thus, as possible sources of cumulative stress, both minority religious group membership and life-changing religious experiences may contribute to conditions that are deleterious for hippocampal volume.

What the authors left unsaid is the other end of the spectrum: the tremendous stress on “no religious affiliation” subjects the non-believers in the current socio-cultural and political environment of the United States which is marked by an apparent spate of religiosity, where areligiosity is facilely equated with amorality.

Therefore, it is possible that chronic stress is responsible for the observed reduction in hippocampal volume. Although the assessed stress levels in subjects didn’t influence the outcome in the current study, the authors indicate that they measured only acute stress, but not the cumulative effects of chronic stress. It may also be difficult for religious people to identify religion as a potential stressor, thereby complicating the assessment.

To summarize, the authors indicate that certain religious factors may be responsible for stress, which may adversely affect the hippocampal volume in those individuals who subscribe to such factors.

As I was reading through the discussion, I was struck by a question about the hypothesis tested in the current study: Is it possible to analyze the same observations from a diametrically opposite perspective? What I mean is this: Is it possible that –

Hippocampal atrophy (or some non-pathognomonic reduction in volume) is age related?

Given that all the subjects were 58+ years in age, the median size of hippocampus measured in non-believers is the right size (baseline) for that age or age-range?

Introduction to religion at an early age, moderate religious feelings, participation in religious rituals and so forth may cause a surge of emotions —especially conflicting emotions and sentiments regarding religion, with increased exposure to different worldviews— which can lead to hippocampal hypertrophy in the believer group?

Those who have experienced LCREs or found religion late (“born-again”) are so firmly adherent to their belief systems, that they no longer experience any doubt, uncertainty or a lack of conviction – and therefore, are not subject to strong emotional upheavals in a chronic manner; as a consequence, their hippocampal volume returns to the baseline?

Would this be a valid alternative hypothesis?

I am not conversant enough with the functional relationship between the organic brain and psychology to know the answer. I have left a comment at the PLoS One page for the article asking the same questions. Perhaps someone else more knowledgeable can illuminate?